This invention relates to an automatic document feeder for supplying, transporting and discharging an original relative to a predetermined position and an image forming apparatus equipped with the automatic document feeder. More particularly, this invention relates to a structure for unitizing sheet supply, transport and discharge mechanisms in an automatic document feeder.
An automatic document feeder mounted on an image reading apparatus is provided with a sheet supply mechanism formed of sheet supply rollers and register rollers for drawing out an original stacked on a sheet supply tray; a transport mechanism having a transport belt for placing the original drawn from the sheet supply mechanism on a platen glass of an image forming apparatus; a discharge mechanism including discharge rollers for discharging the original with an image thereupon read from the transport mechanism to a discharge tray; and a guide for guiding the original. These mechanisms are mounted on a pair of side plates and unitized, and an outer cover covers the unit.
In such a configuration, however, since a large number of parts such as the various rollers and guides are separately mounted on a pair of the side plates, the structure of the apparatus becomes more complex, and the number of assembly steps increases.
Furthermore, the guide mounted to straddle a pair of the side plates is formed of a rigid metallic material to maintain strength of the apparatus, thus an overall weight of the apparatus becomes heavier, creating a problem of poor operability.
On the other hand, as disclosed in Japanese Patent Publication (Tokkai) No. 06-598 or Japanese Patent No. 2939621, in order to have a structure in which an assembly operation is improved, sheet supply, transport and discharge mechanisms are separately unitized and mounted on an outer cover from under the cover, thereby forming a unitized structure with the outer cover as an apparatus frame.
In the apparatus having such a unitized structure, however, since the outer cover is made of a plastic, the apparatus lacks sufficient strength thereof, resulting in a problem of causing deformation of the apparatus itself.
To increase the strength of the apparatus, it is possible to mount a support member, such as a metallic stay, on several locations in the outer cover of the apparatus as reinforcement. However, mounting the support members leads to an increase in an overall weight of the apparatus, preventing reduction in the apparatus weight.
Furthermore, in such a configuration, because the sheet supply, transport and discharge mechanisms are mounted on the outer cover and are unitized, each unit must be removed from the bottom side of the apparatus for maintenance of each part, thereby making the removal work troublesome.
In view of the aforementioned problems, an object of the present invention is to provide an automatic document feeder with a simplified structure to reduce the number of assembly parts, in addition, to provide a lighter and rigid structure.